#DRMPerspective

#DRMPerspective

Hogtown Creek: A Product of Multi-Discipline Collaboration

May 3rd, 2019 by John Minton, Jr., PE, CFM, Chad Rischar, PWS

Hurricane Irma barreled through the state of Florida in 2017, raising water levels across the state. In Alachua County, FL, the sudden rise in water levels was problematic, particularly for Hogtown Creek in Gainesville, FL. The higher flows in the creek were causing the channel to erode, forming a steep bank. That steep bank was nearly compromised and was threatening to undermine NW 16th Avenue, a connector road for the local area, and the associated sidewalk.

Already under a continuing services contract with Alachua County, DRMP brought in a collaborative team that brought multi-discipline experts together to provide a design to resolve the erosion. Initially, the project’s scope included the installation of sheet pile wall to stabilize the steep bank that formed, which would protect the road from being swept off into the creek. But an alternative, more aesthetic, cost-effective solution presented itself when the DRMP team began collecting data for the project. DRMP Senior Environmental Scientist Chad Rischar, PWS, suggested to DRMP’s John Minton, Jr., PE, CFM, the project’s Drainage Engineer, that moving the creek channel away from the road and providing slope protection, instead of installing sheet pile, would keep the natural aesthetics of the Alfred Ring Park that the creek flowed through.

After the DRMP team analyzed the condition of the creek as it winded through the project area, it was determined that the creek had previously flowed further away from the road at some point in history. This conclusion helped the team overcome their biggest challenge: permit acquisition to rehabilitate the creek channel.

Although the design approach didn’t include a sheet piling wall, the team did want to provide an armored slope at a gentle angle away from the creek to protect 16th Avenue during future storm events. We used a multi-tiered armoring design.

Across the channel bottom, a Gabion mattress was designed, to provide a hardened bottom that would protect against the formation of scour holes.

At the middle layer, a near vertical wall of Gabion baskets was designed to protect the slope through any 100-year storm event.

Above the wall, soil bags were used to soften the slope and provide a media for vegetated slope stabilization. Soil bags have a similar appearance to sandbags, but their porous casing allows for plant life to grow from the bags while still providing a soft armoring to protect the slope. The soil bag slope provides armoring of flows up to the 100-year storm event.

The top layer was protected with coconut fiber matting. This provided additional support to re-establish the slope and allowed for native vegetation to be established.

This concerted and revised approach provided a design that integrated well with the park’s natural setting while still preventing erosion to the channel’s slope protecting the nearby road, NW 16th Avenue.

Chad Rischar, PWS and John Minton, Jr., PE, CFM discussed this innovative design further by answering a few questions about the project:

John:

Q: How did you come about working with one another for this project?

A: Chad and I were both tasked with working on the project. I was selected due to my experience working with channel restoration projects, and I’m a local University of Florida grad. Chad was selected since he works out of DRMP’s local Gainesville office, and he has extensive experience working with the local natural resources and regulatory agencies.

Chad:

Q: How did a Drainage Engineer and an Environmental Scientist collaborate to create this innovative design?

A: During the field review, I expressed interest in developing a practical way to design the project other than hard armored sheet piling. I was coming from the thought process that the project was in a natural setting within a recreational City park, which made sense to think of restoration from a different view shed. All members of the team came together and agreed that we needed to find a new and more innovative way to design this project. Since the original scope called for the sheet piling wall, immediate concerns were presented as to how construction of these heavy walls would have minimal impacts due to conflicts such as overhead utilities, temporary closure of 16th Avenue travel lanes and expansive tree coverage. The new design overcame these potential conflicts and provided a better-quality product.

John:

Q: What made this project innovative?

A: One aspect that made the project innovative is that we weren’t afraid to move the channel. I’m sure that some people could’ve seen that as a constraint on the project from the beginning. We had the confidence that we could get the channel moved and permitted, which helped us convince the client and regulatory agencies that this would work.

Chad:

Q: What is the added benefit of working together?

A: Sound boarding initial thoughts and discussing the vision for construction through a concerted effort. I rely on my previous experiences and insights into the permitting aspects of a project. My primary responsibility is to add value to the design from a natural resource protection lens. I’m constantly searching for innovative techniques that decrease natural resource impacts and/or improve the quality of the natural systems through the design and construction phases.

John:

Q: Do you anticipate working together on similar projects in the future?

A: I enjoyed working with Chad on this project. It was good to have an environmental scientist counterpart that brings the expertise that Chad did. We worked together to solve a complex problem and sought a good resolution for the client and the public.

Chad:

Q: Was this cost efficient?

A: Per our early estimates, we projected that the sheet piling would have been near double construction costs. But considering the potential constructability issues that were considered in the field reviews, we determined that construction costs could have been much higher.